Fix issue 1833 by reporting an error if the type is not found.

frog/analyze.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /**
  * A simple code analyzer for Dart.
  *
  * Currently used to ensure all concrete generic types are visited.
  * Also performs all static type checks - so these don't need to be
  * done in later phases.
@@ skipping 583 matching lines @@
       constructorName = names.removeLast().name;
       if (names.length == 0) names = null;
 
       typeRef = new NameTypeReference(
           typeRef.isFinal, typeRef.name, names, typeRef.span);
     }
 
     var type = resolveType(typeRef, true, true);
     if (type.isTop) {
       type = type.library.findTypeByName(constructorName);
+      if (type == null) {
+        world.error('cannot resolve type $constructorName', node.span);
+      }
       constructorName = '';
     }
 
     if (type is ParameterType) {
       world.error('cannot instantiate a type parameter', node.span);
       return _frame._makeValue(world.varType, node);
     }
 
     var m = type.getConstructor(constructorName);
     if (m == null) {
@@ skipping 169 matching lines @@
     for (var item in node.pieces) {
       var val = visitValue(item);
       var sval = val.invoke(_frame, 'toString', item, Arguments.EMPTY);
       ret = ret.binop(TokenKind.ADD, sval, _frame, item);
     }
     return _frame._makeValue(world.stringType, node); //???ret;
     */
   }
 }